Abstract:The WeCare project (Utilizing Weather information for Climate efficient and eco efficient future aviation), an internal project of the German Aerospace Center (Deutsches Zentrum für Luft-und Raumfahrt, DLR), aimed at finding solutions for reducing the climate impact of aviation based on an improved understanding of the atmospheric impact from aviation by making use of measurements and modeling approaches. WeCare made some important contributions to advance the scientific understanding in the area of atmospheric and air transportation research. We characterize contrail properties, show that the aircraft type significantly influences these properties, and how contrail-cirrus interacts with natural cirrus. Aviation NO x emissions lead to ozone formation and we show that the strength of the ozone enhancement varies, depending on where within a weather pattern NO x is emitted. These results, in combination with results on the effects of aerosol emissions on low cloud properties, give a revised view on the total radiative forcing of aviation. The assessment of a fleet of strut-braced wing aircraft with an open rotor is investigated and reveals the potential to significantly reduce the climate impact. Intermediate stop operations have the potential to significantly reduce fuel consumption. However, we find that, if only optimized for fuel use, they will have an increased climate impact, since non-CO 2 effects compensate the reduced warming from CO 2 savings. Avoiding climate sensitive regions has a large potential in reducing climate impact at relatively low costs. Taking advantage of a full 3D optimization has a much better eco-efficiency than lateral re-routings, only. The implementation of such operational measures requires many more considerations. Non-CO 2 aviation effects are not considered in international agreements. We showed that climate-optimal routing could be achieved, if market-based measures were in place, which include these non-CO 2 effects. An alternative measure to foster climate-optimal routing is the closing of air spaces, which are very climate-sensitive. Although less effective than an unconstrained optimization with respect to climate, it still has a significant potential to reduce the climate impact of aviation. By combining atmospheric and air transportation research, we assess climate mitigation measures, aiming at providing information to aviation stakeholders and policy-makers to make aviation more climate compatible.

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Today, the European airspace is already faced with airspace capacity constraints, especially during business driven peak periods of the day in central European air traffic control sectors. This capacity bottleneck will cause a challenging number of severe difficulties in future flight planning and airport ground handling. Additionally, the growing public awareness and the increasing scientific knowledge of the aviation environmental impact urges air traffic stakeholders to reduce the aviation induced global warming to an acceptable level. These efforts should include both the prevention of unnecessary fuel burn due to detours and the avoidance of passing ice-supersaturated regions during cruise to prevent contrail formation. Therewith, conflicting goals have to be considered in trajectory optimization. The induced contrails influence the radiation budget of the Earth atmosphere, which depend on the dynamic size and location of the ice-supersaturated regions. However, contrail avoidance can lead to unsolvable high requirements on airspace capacity in dry and warm air spaces, where contrails are not induced. Furthermore, contrail avoidance procedures can lead to large detours, which in turn cause more fuel burn and an increased impact on the environment due to the emission of additional radiative active substances. In this paper, the Air Traffic Control Fast Time Simulator and Air Traffic Optimizer AirTOp is used to simulate one day of Europeans air traffic and to reduce the radiative forcing of contrails by minimizing the number of flight hours through dynamic ice-supersaturated regions. Rerouting the affected flights does this, so that separation requirements are still fulfilled and each aircraft still reaches its destination. In this paper the following measures are assessed without and with contrail involved rerouting: the decrease of airspace capacity, the additional distance flown, the additional fuel burn and the contrail induced environmental impact. We found, that rerouting on this special day would have caused higher additional fuel and time costs, than saved reduced contrail costs.

Multicriteria trajectory optimisation is expected to increase aviation safety, efficiency and environmental compatibility, although neither the theoretical calculation of such optimised trajectories nor their implementation into today’s already safe and efficient air traffic flow management reaches a satisfying level of fidelity. The calibration of the underlying objective functions leading to the virtually best available solution is complicated and hard to identify, since the participating stakeholders are very competitive. Furthermore, operational uncertainties hamper the robust identification of an optimised trajectory. These uncertainties may arise from severe weather conditions or operational changes in the airport management. In this study, the impact of multicriteria optimised free route trajectories on the air traffic flow management is analysed and compared with a validated reference scenario which consists of real flown trajectories during a peak hour of Europe’s complete air traffic in the upper airspace. Therefore, the TOolchain for Multicriteria Aircraft Trajectory Optimisation (TOMATO) is used for both the multicriteria optimisation of txrajectories and the calculation of the reference scenario. First, this paper gives evidence for the validity of the simulation environment TOMATO, by comparison of the integrated reference results with those of the commercial fast-time air traffic optimiser (AirTOp). Second, TOMATO is used for the multicriteria trajectory optimisation, the assessment of the trajectories and the calculation of their integrated impact on the air traffic flow management, which in turn is compared with the reference scenario. Thereby, significant differences between the reference scenario and the optimised scenario can be identified, especially considering the taskload due to frequent altitude changes and rescinded constraints given by waypoints in the reference scenario. The latter and the strong impact of wind direction and wind speed cause wide differences in the patterns of the lateral trajectories in the airspace with significant influence on the airspace capacity and controller’s taskload. With this study, the possibility of a successful 4D free route implementation into Europe’s upper airspace is proven even over central Europe during peak hours, when capacity constraints are already reaching their limits.

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